Thermionic electron-emissive electrode with a gas-binding material

ABSTRACT

A thermionic cathode including a support in the form of a metal sheet with an electron-emissive coating on one side and a coating of gas-binding material on the opposite side. The sheet may be formed into a tube and the electron-emissive coating may be on the outside or inside and the gas-binding material on the opposite side. Such cathodes may be employed in electric discharge tubes, such as cathode-ray tubes and low-pressure gasdischarge lamps.

United States, Patent Inventor Friedrich Hermann Raymund AlmerEmmasingel, Netherlands Appl. No. 811,846 Filed Apr. 1, 1969 PatentedJune 1,1971 Assignee U.S. Philips Corporation New York, N.Y. PriorityApr. 4, 1968 Netherlands 6804720 THERMIONIC ELECTRON-EMISSIVE ELECTRODEWITH A GAS-BINDING MATERIAL 15 Claims, 7 Drawing figs.

0.8. CI 313/174, 313/l76,3l3/178,313/346 Int. Cl ..H0lj 19/68, H01]19/70 Field of Search 313/174,

[56] References Cited UNITED STATES PATENTS 2,741,717 4/1956 Katz2,843,781 7/1958 Kerstetter et a1. 3 ,078,387 7/1968 Dorgelo 3,110,08111/1968 Hendriks.... 3,495,116 2/1970 Horn et a1 Primary Ex aminer.lohnW. Huckert Assistant ExaminerAndrew .1. James Attorney-Frank R. Trifari313/178 313/178 313/179X 313/346X 3l3/179X ABSTRACT: A thermioniccathode including a support in the form of a metal sheet with anelectron-emissive coating on one side and a coating of gas-bindingmaterial on the opposite side. The sheet may be formed into a tube andthe electron-emissive coating may be on the outside or inside and thegas-binding material on the opposite side. Such cathodes may be employedin electric discharge tubes, such as cathode-ray tubes and low-pressuregas-discharge lamps.

PATENTEUJUN 1m 3,582,702

INVENTOR. FRIEIIRICH H.R.ALMER .BY 2%., 4; K. L

AG NT THERMTONTC ELECTRON-EMHSSIVE ELECTRODE WHTH A GAS-BINDING MATERIALThe invention relates to a thermionic electrode which includes a metalsupport one side of which is provided with an electron emissive coating.Furthermore the invention relates to an electric discharge tube providedwith such an electrode.

Many electrode constructions for electric discharge tubes starting froma supporting body, for example, from metal strip or sheet are known fromliterature. This starting material is preferably chosen because it isadvantageous to have a support having a large surface and a smallvolume. Mostly at least one side of the supporting body is provided withan electronemissive coating. To this end many methods are known, forexample, spraying, immersing, compressing or combinations thereof.

Prior to or after providing the emissive coating the electrode is formedinto its ultimate shape.

in general the discharge space of an electric discharge tube containsdifferent gaseous impurities. These are partly residual gases which haveremained after exhausting of the tube and partly these are gases whichare bound to or in the wall of the discharge tube, the electrodes or thecurrent supply wires and the like, and which evolve during operation ofthe tube. These gaseous impurities are mostly disturbing for thesatisfactory operation of the tube, because they may give rise to apoisoning of the emissive coating. in the case of low-pressure gasdischarge lamps the gaseous impurities may also influence the efficiencyof the lamp in an unfavorable sense. ln addition they may considerablyincrease the ignition voltage of the lamp.

To bind these impurities so that they can no longer exert theirdisturbing influence in the discharge space it is known to providegas-binding materials sometimes also called getters, in the dischargespace. It is, for example, known to form a gasbinding surface on aportion of the wall of the tube, or to place a sheet or strip of agas-binding material in the vicinity of an electrode.

The following requirements are, inter alia, imposed on a getter materialfor a discharge tube. In the first place the material must be able tobind the unwanted gases to a sufficient extend; in the second place thegases must be bound sufficiently quickly. in general the gettermaterials have, however, a selective action, that is to say, they bindonly very specific gases in sufficient quantities and at a sufficientvelocity. in addition the operation of most getters is dependent on thetemperature. Thus, for example, a barium coating will operate at acomparatively low temperature (lower than 100 C.) whereas a solidzirconium or titanium plate operates satisfactorily only at considerablyhigher temperatures (higher than b C.)

A thermionic electrode according to the invention is provided with asupport consisting of metal sheet, one surface of which has anelectron-emissive coating and is characterized in that the other surfaceof the support has a gas-binding coating.

in an electrode according to the invention two functions are combined ina simple manner, namely the supply of a thermally emitted electroncurrent and the binding of the gaseous impurities. ln electrodesaccording to the invention the getter coating and the emissive coatingdo not disturb each other and the two mentioned functions are fulfilledin an efficient manner. it has surprisingly been found that even animprovement of the emissive qualities may occur in case of suitablechoice of the gas-binding material, because the gas-binding material hasan activating effect on the emitter material. ln fact, at the hightemperature at which the electrode is operated part of the gas-bindingmaterial will diffuse through the support of the electrode according tothe invention to the emissive coating, where it forms, for example, freebarium due to reduction of barium oxide. Due to the permanent supply ofactivator material during the lifetime of the discharge tube, theemissive qualities retain their optimum values particularly when thegas-binding action is accompanied by an activating action it is possibleto manufacture discharge tubes having a long lifetime.

The result of providing a getter coating on a thermionic electrode isthat the coating is brought to a high temperature during the operationof the discharge tube. This is very advantageous if gas-bindingmaterials are used, whose gas-binding properties enhance atcomparatively high temperatures.

One or more of the elements zirconium, titanium, lanthanum, cerium orthorium are preferably used as gas-binding materials. All mentionedelements have excellent gasbinding properties at a high temperature.Particularly oxygen, water vapor, carbon dioxide and carbon monoxide arebound to a sufficient extent and at a sufficient velocity by theseelements. Especially these gases have been found to be disturbing duringthe operation of the discharge tube. An advantage of the saidgas-binding elements is that they have a great affinity for hydrogen ata comparatively low temperature. Prior to the discharge tube beingignited, substantially all hydrogen in the discharge space is thus boundto the gas-binding coating. As is known, too high a hydrogen pressure inthe discharge space gives rise to an increase of the ignition voltage.

The form of the gas-binding coating is important for the gasbindingproperties. Thus a foil, of, for example, zirconium provided on thesupport, or a zirconium layer having a small pore volume will have asmaller gas-binding power than a layer of zirconium granules which areonly weakly sintered together. In fact, a weakly sintered layer has alarge active surface.

A method of manufacturing an anode for electric discharge tubes providedwith a gas-binding coating is known from British Pat. Specification No.995,82l. The gas-binding coating is preferably provided on an electrodeaccording to the invention in accordance with this known method. To thisend, metal particles are provided on a metal strip from a holder,whereafter the strip provided with the particles is introduced into afurnace where the particles are sintered to the strip. One or more ofthe above-mentioned gas-binding materials are provided in theinterstices between the metal particles, mostly in the form of hydrides.The coating thus formed is then compressed, for example, between steelrollers so that the metal particles are deformed and this to such anextent that they largely surround the gas-binding material and thereforeretains it. An electrode according to the invention may now be formed,for example, by bending, welding etc. from pieces of the metal striphaving a gas-binding coating and obtained in the manner as describedabove. The emissive coating may be provided on the other side of thestrip prior to or after the ultimate design of the electrode.

Upon so-called formation and activation of the electrode in thedischarge tube the getter material is only weakly sintered so that alarge active surface is maintained. If the getter material is providedin the coating as a hydride, for example, zirconium hydride, thehydrogen gas evolves during formation which enhances the activation andformation of the emissive coating.

It has been found that addition of tungsten and/or nickel powder to thegas-binding material has a favorable influence on the gas-bindingproperties. The tungsten powder prevents too strong a sintering of thematerial and due to the addition of the nickel powder a larger quantityof getter material is incorporated between the metal particles. Theoverall quantity of tungsten and/or nickel is 20-60 percent by weight.

ln one preferred embodiment of an electrode according to the inventionthe emissive coating is provided in the same manner as described abovefor the gas-binding coating. Such a method of providing a thermioniccoating on electrodes is known from British Pat. Specification No.940,063. An electrode is then obtained whose emissive coating has a lowwork function as a result of the weak sintering of the emittingmaterial. The electrode may then be operated at a temperature which neednot be higher than approximately 900 C. in addition this embodiment ofthe electrode has the advantages of a small electric resistance and ofan excellent resistance to sputtering by an ion bombardment possiblyoccurring.

if the two coatings are provided in the manner described above it isrecommended to form initially the gas-binding coating on one side of thestrip and thereafter the emissive coating on the other side, in whichthe sintering of the metal particles for the formation of thelast-mentioned coating must be effected in a reducing atmosphere, forexample, in hydrogen or in a reducing mixture of hydrogen and an inertgas in order to protect the hydrides in the gas-binding coating. It isalternatively possible to provide the two coatings simultaneously.

Satisfactory results have been obtained with molybdenum, nickel-platediron, nickel and so-called cathode-nickel, (nickel which contains one ormore activating elements such as magnesium, aluminum, silicon orzirconium in very small quantities) as materials for the support of theelectrode. Nickel and particularly cathode-nickel are, however,preferred because these materials are cheap and do not contain unwantedimpurities. In addition these materials can easily be processed.

The metal particles sintered to the support may consist, for example, ofvanadium, molybdenum, iron, cobalt or nickel, because these metals cansatisfactorily be sintered to a metal substratum. Here again nickel ispreferred, inter alia because it is cheap and because it can easily beprovided on the support in the desired shape. In fact, when using nickelparticles they can be fed to the strip from a magnetic container so thatthe particles are directed in such a manner that agglomerations areformed in a direction perpendicular to the strip, with mutualinterstices between the agglomerations. Upon sintering along columns ofnickel particles are then formed on the strip which may surround muchgas-binding or electronemitting material.

For the supports in electrodes according to the invention, it isadvantageous to use metal strip which has a slight thickness, forexample, between 20 and 100 m. The electrode then has a slight heatcapacity so that the time required to bring electrodes to thetemperature of emission is short.

To obtain a satisfactory lifetime of the discharge tube the electrodeaccording to the invention is preferably provided with at least 1 mg. ofemitting material per cm. ofthe emitting surface. A quantity of emittingmaterial larger than l mg./cm. is mostly not necessary. One or more ofthe alkaline earth oxides may be used as emitter material in themanufacture of the tube. These oxides are mostly formed carbonates, forexample, a mixture of barium carbonate, strontium carbonate and calciumcarbonate. The emitting material may advantageously be mixed with l l 0percent by weight of one or more of the elements titanium, zirconium,hafnium or thorium. The said elements enhance the process of activationof the emitting material, particularly during the initial operatinghours of the tube. When the admixed activating elements have beenconsumed the diffusion process of the gas-binding material has advancedso far that sufficient activators are post supplied.

An electrode according to the invention in an electric vacuum dischargetube is preferably formed as an indirectly heated cathode having ahollow cylindrical supporting body. The emissive coating is thenprovided on the outer side of the cylinder opposite the anode. Thegetter coating is provided on the inner side of the cylinder and bindsthe gases evolved from the filament so that these cannot penetrate thedischarge space. At least one end of the cylinder has an aperture sothat also the gases evolved elsewhere in the discharge space may bebound by the getter coating. In this use the permanent supply ofactivators from the getter coating to the emissive coating plays a greatpart so that tubes having a very long lifetime can be manufactured.

When using an electrode according to the invention in cathode-ray tubes,for example, for television purposes, the electrode is preferably formedas an indirectly heated cathode having a hollow cylindrical supportingbody one end of which is closed by a metal sheet whose outer side isprovided with an emissive coating. The getter coating is provided on theinner side of the sheet and possibly on the cylindrical portion of thesupport.

An electrode according to the invention may very advantageously be used,in a low-pressure gas discharge tube, for example, a low-pressuremercury vapor discharge lamp. Here again the electrode preferably hasthe shape of a hollow cylinder at least one end of which has an apertureIn this case the emissive coating is provided on the inner side of thecylinder. The electrode material possibly sputtered by an ionbombardment then will not escape easily from the electrode. The gettercoating is now provided on the outer side of the cylinder which isadvantageous for the gas-binding action because the getter coating isthen easily accessible to the impurities.

The invention with reference to the accompanying drawing, in which:

FIG. 1 is a cross-sectional view of an electrode according to theinvention,

FIG. 2 is a cross-sectional view of a further embodiment of an electrodeaccording to the invention,

FIG. 3 is a sectional view of nickel strip provided with a gas bindingand an emissive coating which strip can be used in the manufacture of anelectrode according to the invention,

FIG. 4 shows a further embodiment of an electrode according to theinvention for use in cathode-ray tubes,

FIG. 5 is a sectional view of a vacuum discharge tube according to theinvention, and

FIG. 6 is a sectional view of a cathode-ray tube according to theinvention,

FIG. 7 finally shows a low-pressure mercury vapor discharge lampaccording to the invention.

In FIG. 1, the reference numeral 1 indicates the supporting body fromnickel strip of a hollow cylindrical electrode which may be used invacuum discharge tubes. The dimensions of the support are dependent onthe purpose for which the electrode is used. In a rectifier diode, forexample, the length of the cylinder may be 60 mm. and the diameter maybe 5 mm. The thickness of the strip is 75 am. in this case. Thegas-binding coating 2 is provided on the inner side and the emissivecoating 3 is provided on the the outer side of the electrode. A lockseam is indicated by 4 which in this embodiment of the electrode islocated on the inner side.

FIG. 2 shows the cross section of a hollow cylindrical electrode for usein a low-pressure gas discharge lamp, the supporting body 1 of nickel is15 mm. long and has a diameter of approximately 2.5 mm. while thethickness of the nickel strip is approximately 50 m. In this case thegas-binding coating 2 is provided on the outer side and the emissivecoating 3 is provided on the inner side of the support. The lock seam 4now extend along the outer side of the electrode.

FIG. 3 shows on an enlarged scale a cross section of part of anelectrode according to the invention. Reference numeral 1 indicates astrip of cathode-nickel which contains, for example, 0.030.09 percent byweight of magnesium, and which serves as a support for the gas-bindingcoating 2,5 and the emissive coating 3,6. In this case the strip has athickness of approximately 50 pm. The two coatings are approximately 10m. thick. The gas-binding material 2 consists of zirconium to whichapproximately 30 percent by weight of nickel is added and it is largelysurrounded and retained by the columns 5 of nickel particles and thenickel strip 1. The emitting material consists of a mixture of alkalineearth oxides to which 1-10 percent by weight of titanium and/orzirconium is added and it is largely surrounded by the columns 6 ofnickel particles and the nickel strip 1. After the electrode hasoperated for some time, the nickel support will contain a small quantityof zirconium. The concentration of the zirconium in the supportdecreases, while going from the gas-binding surface to the emittingsurface. After some time a stationary state sets in, the supply ofzirconium to the emitting coating being exactly sufficient for anoptimum action of this coating.

FIG. 4 shows the support 1 from nickel strip of an electrode which isused in a cathode-ray tube, for example, for the display of televisionpictures. The support consists of a hollow cylinder closed at one endand formed from one one piece of the nickel strip by deep drawing. Thegas-binding coating 2 is provided across the entire inner surface of theelectrode. The emissive coating 3 is provided on the outer side of theelectrode and extends substantially throughout the surface of theportion closing the cylinder. The electrode is mostly used incombination with a metal shaft which surrounds the filament and which isnot shown in the drawing.

FIG. 5 shows the glass envelope 7 of a triode according to theinvention. The cathode l, 2, 3 has a shape as shown in FIG. 1 and isindirectly heated by a filament spiral 8. A grid is indicated by 9 andan anode is indicated by 10.

F IG. 6 shows a cathode-ray tube according to the invention which isused for the display of pictures. The indirectly heated electrode 1provided with an emitting surface 3 and a gasbinding surface 2 is of thetype as shown in FIG. 4. The filament is not shown. The electrode issecured with the aid of ceramic material 14 in a so-called Wehneltcylinder 15. This cylinder and the remaining electrodes not shown in theFigure are supported by supporting columns 16. The envelope, forexample, of glass of the discharge space is indicated by 7.

ln HO. 7 reference numeral 7 indicates the wall, for example, of glassof a low-pressure mercury vapor discharge lamp according to theinvention which lamp consumes a power of 40 watt during operation. Apinch 11 is formed at either end of the lamp through which currentsupply wires 12 are passed. The current supply wires are connected inthe discharge space to electrodes 1, 2, 3 by means of spot-welding. Across section of these electrodes is shown in FlG. 2. A luminescentlayer is indicated by 13. The electrode construction is cheap and doesnot require means to preheat the electrode upon ignition of the lamp.

What 1 claim is:

l. A thermionic electron-emissive electrode comprising a supportconsisting of metal sheet, an electron-emissive coating on one surfaceof said support, and a coating of a gas-binding material on the oppositesurface of said support.

2. A thermionic electron-emissive electrode as claimed in claim 1,wherein the support has a thickness of between and 100 **m.

3. A thermionic electron-emissive electrode as claimed in claim llwherein the gas-binding material is also an activator for the emissivecoating.

4. A thermionic electron-emmissive electrode as claimed in claim 1wherein the gas-binding material consists of an element selected fromthe group consisting of one zirconium, titanium, lanthanum, cerium andthorium.

5. A thermionic electron-emissive electrode as claimed in claim 1wherein the gas-binding material is mixed with 2060 percent by weight ofat least one of the powders of tungsten and nickel.

6. A thermionic electron-emissive electrode as claimed in claim 1wherein the gas-binding coating consists of metal particles sintered tothe support between which the gas-binding material is provided, themetal particles substantially surrounding the gas-binding material.

7. A thermionic electron-emissive electrode as claimed in claim Iwherein the electron-emissive coating consists of metal particlessintered to the support between which emitting material having a workfunction smaller than 2 ev. is provided, the metal particles having ashape such that they largely surround the emitting material.

8. A thermionic electron-emissive electrode as claimed in claim 1wherein the metal support consists at least in part of nickel.

9. A thermionic electron-emissive electrode as claimed in claim 7wherein the metal particles consist of nickel.

10. A thermionic electron-emissive electrode as claimed in claim 9wherein the electrode contains at least of 1 mg. of emitting materialper cm. of emitting surface.

11. A thermionic electron-emissive electrode as claimed in claim 9wherein the emitting material consists of at least one alkaline earthoxide.

12. A thermionic electron-emissive electrode as claimed in claim 11,wherein the emitting material is mixed with 1-10 percent by weight of atleast one of the elements selected from the group consisting oftitanium, zirconium, hafnium and thorium.

13. An electric discharge tube including a thermionic electron-emissiveelectrode comprising a hollow cylinder at least one end of which has anaperture, an emissive coating provided on the outer surface of thecylinder, and a getter material on the inner surface of the cylinder.

M. A cathode-ray tube including a thermionic electron emissive electrodecomprising a hollow cylinder one end of which is closed by a metalsheet, the outer side of said cylinder being provided with an emissivecoating and the inner side of the cylinder being provided with agas'binding coating.

15. A low-pressure gas-discharge lamp comprising a thermionicelectron-emissive electrode comprising a hollow cylinder at least oneend of which has an aperture, an emissive coating provided on the innerside of the cylinder, and a gasbinding coating on the outer surface ofsaid cylinder.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated June 1,

Patent No. 3 y 58 2 702 Friedrich Hermann Raymund Almer Inventor(s) Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 42, "extend" should read extent Column 4, line 13, after"invention" insert will now be "**m" should read um described Column 5,claim 2,

Signed and sealed this 18th day of January 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Acting Commissioner of PatentsAttesting Officer FORM po'wso USCOMM-DC 60376-P69 Q U 5 GOVERNMENTPRINYINE OFFICE 959 0-365'334

1. A thermionic electron-emissive electrode comprising a supportconsisting of metal sheet, an electron-emissive coating on one surfaceof said support, and a coating of a gas-binding material on the oppositesurface of said support.
 2. A thermionic electron-emissive electrode asclaimed in claim 1, wherein the support has a thickness of between 20and 100 m.
 3. A thermionic electron-emissive electrode as claimed inclaim 1 wherein the gas-binding material is also an activator for theemissive coating.
 4. A thermionic electron-emmissive electrode asclaimed in claim 1 wherein the gas-binding material consists of anelement selected from the group consisting of one zirconium, titanium,lanthanum, cerium and thorium.
 5. A thermionic electron-emissiveelectrode as claimed in claim 1 wherein the gas-binding material ismixed with 20- 60 percent by weight of at least one of the powders oftungsten and nickel.
 6. A thermionic electron-emissive electrode asclaimed in claim 1 wherein the gas-binding coating consists of metalparticles sintered to the support between which the gas-binding materialis provided, the metal particles substantially surrounding thegas-binding material.
 7. A thermionic electron-emissive electrode asclaimed in claim 1 wherein the electron-emissive coating consists ofmetal particles sintered to the support between which emitting materialhaving a work function smaller than 2 ev. is provided, the metalparticles having a shape such that they largely surround the emittingmaterial.
 8. A thermionic electron-emissive electrode as claimed inclaim 1 wherein the metal support consists at least in part of nickel.9. A thermionic electron-emissive electrode as claimed in claim 7wherein the metal particles consist of nickel.
 10. A thermionicelectron-emissive electrode as claimed in claim 9 wherein the electrodecontains at least of 1 mg. of emitting material per cm.2 of emittingsurface.
 11. A thermionic electron-emissive electrode as claimed inclaim 9 wherein the emitting material consists of at least one alkalineearth oxide.
 12. A thermionic electron-emissive electrode as claimed inclaim 11, wherein the emitting material is mixed with 1-l0 percent byweight of at least one of the elements selected from the groupconsisting of titanium, zirconium, hafnium and thorium.
 13. An electricdischarge tube including a thermionic electron-emissive electrodecomprising a hollow cylinder at least one end of which has an aperture,an emissive coating provided on the outer surface of the cylinder, and agetter material on the inner surface of the cylinder.
 14. A cathode-raytube including a thermionic electron-emissive electrode comprising ahollow cylinder one end of which is closed by a metal sheet, the outerside of said cylinder being provided with an emissive coating and theinner side of the cylinder being provided with a gas-binding coating.15. A low-pressure gas-discharge lamp comprising a thermionicelectron-emissive electrode comprising a hollow cylinder at least oneend of which has an aperture, an emissive coating provided on the innerside of the cylinder, and a gas-binding coating on the outer surface ofsaid cylinder.